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But Trees Can Grow on Money: Blue Plains WWTP Tour

August 18, 2015

The Blue Plains Wastewater Treatment Plant in Washington DC manages biosolids with thermal hydrolysis (small silver tanks) and anaerobic digestion (large tan tanks). The solids can be composted with shredded currency (top right) for indirect P reuse as a soil amendment (middle right).

In my interest to learn about phosphorus recovery from wastewater, I recently toured the Blue Plains Advanced Wastewater Treatment Plant located in Washington DC. Since it serves the nation’s leaders, the plant operators see themselves as being leaders in implementing the paradigm shift from wastewater treatment to resource recovery. The plant collects 370 million gallons each day from the District of Colombia and parts of Virginia and Maryland. The water is treated to meet stringent carbon and nutrient requirements before discharging into the Potomac River just downstream of the Kennedy Center for the Arts and the Thomas Jefferson Memorial. They are most proud of their newly commissioned biosolids management train.

The goals of the system upgrade was to reduce the volume of solids for hauling, increase the marketability of the remaining biosolids, and recover energy. To that end they installed four anaerobic digesters that each hold 3.8 million gallons. The system includes a thermal hydrolysis pretreatment system that handles 450 dry tons per day of feed sludge to improve solids degradation and methane production in those digesters. Thermal hydrolysis heats and pressurizes the solids to provide pathogen reduction and achieves class A biosolids. Then when the pressure is released into the anaerobic digesters, the remaining cellular material “pops”, similar to what happens when you open a can of soda. The energy from the increased methane production from digesting these broken cells is captured by a 10 megawatt steam turbine generator that offsets the energy demand for the thermal hydrolysis.

My eye of course was tracking the phosphorus through the plant. A majority of the influent P would end up in the anaerobic digester supernatant in a concentrated inorganic form. This flow would be the single best point to implement a direct P recovery process. Unfortunately, this opportunity is missed, and the supernatant is simply sent back to the head of the treatment plant. It is perhaps telling to the P sustainability community that the world’s largest advanced wastewater treatment plant, which prides itself on resource recovery, chose to focus on energy and not on nutrients. That indicates that current P recovery technologies simply do not yet yield the necessary economic or regulatory benefits for widespread adoption.

On a positive note, P is indirectly recovered from the second best place: the resulting biosolids. These solids are trucked to the neighboring states for agricultural land application. The class A designation means they have very low pathogens and odor and can be widely used as a fertilizer, where the organic and inorganic P can become incorporated into the soil and taken up by crop plants. They are actively working to develop an even higher value product from these remaining solids though, and the current frontrunner is composting it to produce a marketable soil amendment. In what I consider infinitely ironic, the solids are low in carbon content and must be blended with an organic substrate. They are experimenting with mixing different types of bark, sawdust, and even shredded currency from the Bureau of Printing and Engraving. So while the Blue Plains Advanced Wastewater Treatment Plant doesn’t yet recover P (since money doesn’t grow on trees), it is possible that together with P your trees can grow on money.

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Output of P RCN Meeting in D.C., May 2015

June 18, 2015

On May 18-21, 2015, scientists of the P Sustainability Research Coordination Network (RCN) reconvened in Washington, D.C. for the third annual P RCN meeting. In this meeting, the P RCN moves on from Phase I’s focus on the two P sustainability challenges of “improving P efficiency in food production” and “developing robust pathways of P recycling”. Phase II integrates these two challenges into and theme aimed at “integrating efficiency and recycling to create a sustainable fertilizer system”.

The stakeholder event, “The Future of Phosphorus”, held jointly with the new North American Partnership for Phosphorus Sustainability (NAPPS), took place on May 19. The keynote speaker, Nancy Rabalais, gave a presentation on the hypoxic zones—the aquatic “dead zones” with low levels of dissolved oxygen in the Gulf of Mexico. Then three expert panels, P management and water quality, P recycling, and P sustainability in food production, created a platform for dialogue among scientists, leaders from industry, U.S. government, and non-governmental organizations to discuss needed solutions for P sustainability. Following the panel discussion, stakeholders and scientists broke out into small groups to envision scenarios for transitioning to P sustainability.

The feedback P RCN received from the stakeholder event was then used by the RCN in the rest of the meeting, shaping the direction of research forming in Phase II. At the end of P RCN meeting, four new synthetic “umbrella” groups were formed. 1.  Metrics group—reviewing, developing, and adopting metrics for P sustainability; 2.  Future – Technologies group—informing future technologies and business models, using a solutions-oriented approach; 3.  Transitions Group—identifying barriers and opportunities to a circular economy of sustainable P in agriculture and urban interface; 4.  Ecosystem Services, Nexus and Meta-analysis group—optimizing sustainable P management to provide better ecosystem services.

These research groups are now working on these new topics and will reconvene in Tempe, Arizona in the coming winter. Let’s look forward to this new phase of solving P sustainability challenges.

Urinals Save the Day

June 16, 2015

My longtime friend and college roommate is one of four sons in his family.  His mother got so sick of cleaning the bathroom that served these inaccurate marksmen growing up that she installed a urinal.  It became so famous that all the boys in the neighborhood would find excuses to come use “the target that cannot be missed”, and to this day it’s the only urinal I know of that’s in a private residence.  His mother still credits it as the device that saved her sanity.

Now I propose that urinals have the power to save not just one parent’s plea to contain the pee, but the entire world’s struggle to manage its P.

In a previous post we’ve discussed the merit to source separation as an important step in P recovery from wastewater.  Urine contributes over half of the P found in wastewater (and three-fourths of the nitrogen).  Source separation is the idea of partitioning out the urine before it gets diluted and mixed with all of the other unpleasant things found in municipal wastewater, greatly increasing the efficacy of recovery technologies.  The question is how exactly we do that.

In 2007, Brad Allenby proposed a number of guidelines for making changes to global systems in the Environmental Science & Technology article Earth Systems Engineering and Management: A Manifesto.  The P cycle counts as an earth system under his definition because it is global in scale, highly integrated with other systems, and adapts over time.  Some of those guidelines include making dual function changes that allow for withdrawal, gaining stakeholder support by making decisions transparent, and making only controlled and incremental changes.

Using urinals as source separation instruments is a great way to better manage P in wastewater according to these principles.  Urinals capture the urine and can divert it to a separate waste stream, ideally to be processed locally for P (and N!) capture and reuse.  This would serve the dual purpose of reducing flows of wastewater collected at centralized wastewater treatment plants.  Even if the P recovery strategy did not work out, the infrastructure investment would still pay off due to lower operating costs at the plant.  Stakeholder support is also easy to build, as urinals are apparatus with which users are already familiar and comfortable.  Alternate source separation approaches available to date often require unfamiliar interaction from the user, which is likely to fail in such an intimate setting.  Of course employing urinals only can affect up to half of the human population (those with a Y chromosome), but that is consistent with making only controlled and incremental changes.

Employing urinals as source separation apparatus for improved P recovery is an effective first step to manage P as an earth system, and might just save the sanity of a few parents out there too.

The Case for Source Separation

April 1, 2015


Source separation is a major intervention currently proposed in nutrient management with major potential to improve P reuse.  Source separation refers to keeping liquid human waste separate from solid human waste at the source.  Apparatus that can achieve this are varied, and my favorite one will be the topic of my next post.  Perhaps a familiar example is a toilet where you pull up on the handle for “number 1”, and push down for “number 2”.  Besides the additional benefit of water use optimization, this trick may be a great step to better utilize nutrients and improve P recovery.


The reason behind this is that urine contributes 50% of the P that reaches a wastewater treatment plant, not to mention 80% of the nitrogen and 90% of the potassium (Larsen 2001).  As collected at the source, urine is easily sterilized and has a high concentration of the essential nutrients.  This makes it very easy to achieve a high efficiency for any number of P recovery technologies.  It can even be reused directly after a simple sterilization as a fertilizer and partially offset demand for chemical fertilizer.


However the current method of sanitation in many developed countries does not keep the high-value, nutrient-rich urine separate from the rest of the wastewater.  It first mixes with fecal matter, which adds highly complex constituents with large organic content.  These constituents interfere with P recovery technologies, drastically lowering their efficacy without some sort of pretreatment.   Next the wastewater is highly diluted when mixed with shower and washing machine drains, not to mention many old cities that still have combined wastewater and stormwater sewers.  This drops the nutrient concentration and again lowers nutrient recovery technology efficacy since the process has to look a lot harder to find the P molecules it is trying to catch.  These challenges are just further complicated when industrial contaminants are considered.


Social, infrastructure and technical challenges do exist to implementing source separation.  Source separation toilets can be unfamiliar to users and face social backlash.  It may also require a large infrastructure investment to have piping and collection systems to maintain separation.  This may indicate that dispersed treatment options such as on-site use or storage is more practical than centralized treatment.


Taken together, it makes strong sense from a nutrient reuse perspective to institute source separation.  Increasing ability to recover P improves global food security through providing increasing availability of soil nutrients, reducing reliance on depleting P reserves, and having widespread availability independent of geopolitical influences.


Researchers have a role to play in decreasing inequality in access to phosphorus: Thoughts from the Sustainable Phosphorus Summit

January 15, 2015

Author:  Genevieve Metson

Phosphorus as a major concern

From September 1st to September 3rd 2014, scientists from around the world met at the Sustainable Phosphorus Summit 2014 in Montpellier to discuss how to better manage Phosphorus, an essential element for all of us Over the three-day conference, we heard about some of the cutting edge research on both problems and solutions associated with phosphorus management, from soil-plant interactions to regional changes in human diets.

One of the big problems, which many at the conference thought deserved more attention, is inequality of access to phosphorus. In a workshop session on the last day of the conference, 25 of us gathered and decided to think about what role we, as researchers from diverse disciplines, countries, and levels of experience, can play in addressing this problem. We decided to do so by contextualizing the role of researchers within the priorities of phosphorous producers and phosphorus consumers in the development of more equitable phosphorus management.

Setting the stage: What is the phosphorus inequality problem?

Although the vast majority of mined phosphorus reserves are in Africa (mostly in Morocco), farmers on this continent often have the highest need for P fertilizer and the least access. There are high phosphorus requirements for agriculture because most of the soils are old and high in other elements, like iron or aluminum, that make it difficult for plants to get to the phosphorus that is applied. In addition, as fertilizer applications have been low for many years, there are no reserves in the soil. Access to fertilizers is difficult for farmers because costs are high (due to transportation difficulties and limited market development), and their purchasing capacity is low due to low incomes. On the other hand, many other areas of the world with more incomes have been applying excess phosphorus for years. Sustainable phosphorus management entails not only limiting pollution, it also means ensuring that all farmers have access to enough phosphorus to ensure local and global food security. Currently poorer nations, especially in Africa, are far from having access to the phosphorus they need, leading to a situation of inequality.

The workshop: How can researchers help address the problem?

There is almost no pressure or driver for phosphorus producing countries and companies to change production or marketing processes or business models as long as they have access to the resource and can sell phosphorus at a good price. Requiring a firm target for use of recycled products in fertilizer production and encouraging enterprise development for local and small-scale production could be a way forward. This entails not only changing the market, but also changing what it means to be a “producer of phosphorus”. This new definition could include phosphorus reuse enterprises and small producers. Such a shift could lead to local redistribution of power with regards to phosphorus availability and would enable leveraging the co-benefits between phosphorus management, sanitation, and food security (to name a few), and as such address multiple local priorities at once.

The primary concerns of phosphorus consumers (including phosphorus importing countries and individual farmers) moving forward are related to understanding the diversity of the phosphorus resources and the security of supply. Access to phosphorus resources should be tailored to each specific region, country, and context so that consumers can have access to the forms of phosphorus they can afford and the quantities that can help ensure high yields and limited environmental damage.

Research needs to support efforts towards recycling in order to promote a more equitable redistribution (and decentralization) of resources to ensure access to phosphorus for all farmers. We need to develop easy and low-cost tests and tools that make it possible to assess phosphorus needs and availability of resources at various scales. Such tests would enable more equitable access to information. We, as researchers, should also support more partnered research among nations, farms, and cities across the spectrum of phosphorus accessibility contexts. Specifically initiating research projects that include partnerships across currently phosphorus-rich areas of the world to phosphorus-poor areas would be an important step forward.

The summary above was written by the author and may not reflect all the opinions or perceptions of those that participated in the workshop. Dr. Metson would like to thank Dr. Tina Neset-Smid, Jessica Shepard, Rosanna Kleeman, and Zenah Bradford-Hartke for their help facilitating and documenting the workshop session

Twelve Steps to P Recovery

December 19, 2014

Tens of thousands of people worldwide have overcome addiction using the Twelve Step Program originally proposed by Alcoholics Anonymous in 1939.  They have used these guiding principles to overcome deep challenges, and may have a lesson to teach the world about breaking its dependence and misuse of finite stores of phosphate.   Here we discuss a few of the most pertinent steps, and how they may illuminate a path to a sustainable phosphorus future.

Step 1: Admission. Gaining wide acceptance that we have a phosphorus challenge, and that we are the ones causing it is the first step toward a sustainable phosphorus future.  Humans, not nature, are now the primary driver behind cycling in the phosphorus system.  We liberate more than 20 million tons of phosphate rock each year, more than seven times the natural geochemical rate (1).  Since the earth can only recycle phosphorus lost to aquatic systems on the timescale of millennia, we must admit that we are the only ones who can fix this disconnect.  Saying that we have enough for now and that we’ll figure it out before it becomes a problem is just delaying solutions.  Admitting we face a challenge enables us to strive to implement the solutions.

Step 4: Inventory. Taking a searching, or comprehensive, inventory of our phosphorus situation is a process that is well underway and needs to continue.  The last decade has seen great increases in understanding the quantity and quality of phosphorus ore available, where the mined phosphorus is used, and tracking it through environmental and industrial systems.  Critical information still to be gathered includes understanding where phosphorus flow inefficiencies occur, characterizing known sinks, and evaluating policies and regulations that effect phosphorus cycling whether they are directly aimed at nutrients or not.

Step 5: Mentorship. There are lessons to be learned from previous environmental resource challenges that have successfully been overcome.   We have shifted away from previous dependence on chlorofluorocarbons in refrigerants, lead in solder or paint, and dioxins in insulation for example.  These followed a path from scientific investigation to international conventions and protocol, demonstrating a roadmap for sustainable phosphorus.  Unique to the phosphorus challenge is that no viable substitute exists, barring the simple solution of ‘stop using it and find something else’.  However the experience gained will enable completion of becoming a mentor in Step 12, informing other difficult-to-replace limited resources like oil and coal.

Step 9: Amends. Now that we have embraced and characterized the challenge, we can start to make things right.  New technologies allow for phosphorus efficiency in agriculture and recovery from waste streams, but need to be employed at scale sufficient to rectify the problem.  Policies and protocols at global and regional scale can be enacted to make meaningful change, providing for a more secure food future.  Taking inspiration from the Twelve Steps can lead to recovery from phosphorus misuse.

More on Alcoholics Anonymous at

1) Falkowski, P. et al. Science 290, 291–296 (2000).

SOIL in Haiti

December 16, 2014

In Haiti, a unique enterprise was created that improves public health while contributing to P cycling. SOIL (Sustainable Organic Integrated Livelihoods)  was created in 2006 in order to both improve access to sanitation, and create a sustainable source of fertilizer for Haitian agriculture. Using principles of ecological sanitation (EcoSan), they created toilets and a collection/maintenance business that turns a waste problem into a sustainable fertilizer business. With toilets serving nearly 7,000 Haitians, and a “Poopmobile” transporting waste to composting yards, they are creating thousands of gallons of nutrient rich compost each week.


SOIL uses a social business model in which households rent an EcoSan toilet (marketed as “EkoLakay” locally, a play on the Haitian Creole words for ecological sanitation, “EkoSan,” and house, “Lakay”) for $5 USD per month. Wastes from the EkoLakay toilets are collected weekly and transported to SOIL’s composting waste treatment facility. According to Shannon Smith, Program Assistant at SOIL, the composting process exceeds the World Heath Organization’s standards for the safe treatment of human waste, and cranks out sanitary compost after 6 months

With nearly 50% of all food consumed in Haiti imported, and the cost of fertilizer posing a barrier to farmers, SOIL is demonstrating the feasibility (and profitability!) of small gardens and fertilizing through locally sourced compost.  Heineken has taken notice of SOIL’s efforts, and recently purchased 70,000 gallons of compost for its sorghum farmers in Haiti. With a viable business model continuing to show success, and demand for both toilets and compost, SOIL is poised to continue growing and expanding access to sanitation while contributing to a Sustainable P system.

SOIL photo1

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